Crop gathering devices for collecting crops arranged in windrows can include a belt positioned along the front of the device. The belt is driven to rotate between opposed pairs of roller assemblies to convey the crops into a header that is secured to an agricultural harvester, such as a combine which is directed along the windrow. One or more wheels is located near the belt opposite the header to maintain a spacing between the belt and the ground that most effectively conveys crops onto the belt.
During operation of the harvester, for reasons including uneven terrain and velocity of the harvester, the spacing between the belt and the ground can deviate from an optimum crop conveying position. In response, springs have been positioned between the crop gathering device and the header. While use of springs can help reduce such deviations, forces applied by the springs changes in response to changes in length of the springs (in accordance with Hooke's Law).
What is needed is a suspension system that provides a substantially constant force between the crop gathering device and the header over the range of movement between the crop gathering device and the header.